“…the life which is unexamined is not worth living”

Socrates addresses the jury about to sentence him to death:

Someone will say: Yes, Socrates, but cannot you hold your tongue, and then you may go into a foreign city, and no one will interfere with you? Now I have great difficulty in making you understand my answer to this. For if I tell you that this would be a disobedience to a divine command, and therefore that I cannot hold my tongue, you will not believe that I am serious; and if I say again that the greatest good of man is daily to converse about virtue, and all that concerning which you hear me examining myself and others, and that the life which is unexamined is not worth living – that you are still less likely to believe. And yet what I say is true, although a thing of which it is hard for me to persuade you.
— The Apology, by Plato